Many online communities now employ introductory incentives to attract new users and motivate user contributions, but the benefit of such incentives is still unclear. We draw on a policy change in a large online health community to explore the impact of short-term introductory incentives. We find that even though introductory incentives increase contribution quantity during the policy window, such incentives can significantly decrease it after the policy. The policy also harms the community by lowering contribution quality. However, introductory incentives can increase user retention and thus induce more contribution over the lifecycle of users. Moreover, the effects of such incentives are contingent on users’ offline seniority, which creates opportunities for the platform to target different user groups. This research contributes to the literature on identifying the impact of introductory incentives and intertemporal change of monetary incentives in online communities. The findings also provide novel insights for incentive-driven online communities.